Surecom SW-102: What it tests, how it tests

[Webslinger]

Trying to better understand how and why this tool would be used for my GMRS HT radio. The way I understand it - forgive me if I use the wrong jargon here - the SWR meter is used to test the transmission power of the HT vs the signal gain of the antenna to see how balanced/matched they are? So, a 1:1 ratio is perfect, and anything close to that number is good? What exactly do you call the process for checking that 1:1 ratio, signal to power ratio? I dunno. 

Also, when using the SWR meter for testing, what is the purpose of a dummy load? Is that used only when testing transmission power (wattage), or is that used when testing for that 1:1 ratio? Is the dummy load always used with the meter when testing?

 

Thanks.

[SteveShannon]

6 minutes ago, Webslinger said:

Trying to better understand how and why this tool would be used for my GMRS HT radio. The way I understand it - forgive me if I use the wrong jargon here - the SWR meter is used to test the transmission power of the HT vs the signal gain of the antenna to see how balanced/matched they are? So, a 1:1 ratio is perfect, and anything close to that number is good? What exactly do you call the process for checking that 1:1 ratio, signal to power ratio? I dunno. 

Also, when using the SWR meter for testing, what is the purpose of a dummy load? Is that used only when testing transmission power (wattage), or is that used when testing for that 1:1 ratio? Is the dummy load always used with the meter when testing?

 

Thanks.

The SW-102 measures three things:

frequency

forward power

reflected power. 
 

The forward power and reflected power are used to calculate the SWR, or standing wave ratio. The calculated number is the number to the left of the colon in the SWR. 
 

Reflected power occurs when there is an impedance mismatch. That reflected power doesn’t enter the antenna. It bounces off the transition between the two impedances just as light is reflected from the surface of a lake. 
 

The nominal impedance of your radio is about 50 ohms, so your transmission line must be 50 ohms and so must your antenna. 
But simply being 50 ohms doesn’t make an antenna efficient. It just removes one cause of inefficiency in getting the signal to the antenna. You can have a perfect 1.0:1 SWR but have an antenna that just doesn’t radiate RF. 
 

. 

[Lscott]

4 minutes ago, Sshannon said:

But simply being 50 ohms doesn’t make an antenna efficient. It just removes one cause of inefficiency in getting the signal to the antenna. You can have a perfect 1.0:1 SWR but have an antenna that just doesn’t radiate RF. 

A 50 ohm dummy load will give you a perfect 1:1 match, but nothing radiates from it.

 

[Lscott]

22 minutes ago, tweiss3 said:

Also, on an HT, you never really get an accurate measurement. Sure, it comes with the ground plane plate to attach, and it helps with the measurement, but you end up using adapters, etc. and it never shows accurately. Rotate or tilt the radio 10 degrees and the readings change. 

BTW, on an HT, you shouldn't worry about SWR, if the antenna is the correct band split for your frequencies, just go with it. 

Also consider the environment a typical HT is used in. hand-held, mobile with external antenna, hanging on a belt, stuck in a utility vest pocket. All those will really screw up the SWR.

I was looking at the spec's for some of the hybrid RF power blocks used in many HT's and some mobile radios a while back. The HT one's I've seen they're rated to work up to a max SWR of 20:1!! Basically no antenna. It sort has to be that way due to the highly unpredictable environment HT's have to work in without failure. See example file attached. Look at the first page at the bottom.

M67799MA.pdf

[tweiss3]

Also, on an HT, you never really get an accurate measurement. Sure, it comes with the ground plane plate to attach, and it helps with the measurement, but you end up using adapters, etc. and it never shows accurately. Rotate or tilt the radio 10 degrees and the readings change. 

BTW, on an HT, you shouldn't worry about SWR, if the antenna is the correct band split for your frequencies, just go with it. 

[WRYZ926]

I've never gotten a really good SWR reading on my HT antennas when using the Surecom SW-102 for the reasons already mentioned. I do get good SWR reading when I use my Comet CA-500 antenna analyzer though. The Comet is bigger than HT's with a nice flat surface where the antennas mount. But I still get higher SWR readings on some HT antennas with the Comet analyzer yet they work just fine when attached to the radios.

As others have said, don't rely on testing HT antennas for SWR, you can get misleading results. 

[Webslinger]

Great info and thanks to everyone that responded. I know more now, and I won't fret so much about my HT SWR readings. That will change when the day comes I setup a base station.